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Limits of Composition of Coals (Gruner)
(The values refer to dry, ashless coal)
Appearance and Quality Q£ ^jjg Coke
O + N
Caked but very
or gas coal
Fat, caking or
Caked and com-
or caking coal
Adherent or pul-
or anthracitic coal
The calorific power of coals, referred to the dry, ashless fuel, varies in general
from 7600 to 8900 cals.
As regards the uses to which different coals are especially suited, long flame,
non-caking coal (Class i) is adapted to the manufacture of gas and particularly
for reverberatory furnaces. Gas coal (Class 2) is preferred for making gas, since,
in comparison with the preceding, it gives volatile matters richer in carbon
and hence more illuminating, although in lower yield. Fat, caking or furnace
coal is suitable for use in reverberatory furnaces and for making metallurgical
coke ; for the latter purpose the short-flame caking coals are particularly adapted.
Finally, the lean, short-flame or anthracitic coals and the anthracites, owing
to their slow combustion and to the little smoke they give, are used for domestic
purposes and for the heating of boilers, where a slow, quiet fire is required.
Further, in consequence of the paucity of their volatile matters, the anthracites
may be used directly in blast furnaces instead of coke.
For industrial purposes coal should not contain more than 2-3 % of sulphur.
The best coals contain 3-8% of ash and the proportion may be 12% in good
coal, but coal with more than this is regarded as medium or bad. The moisture
of unwashed coal should not exceed 3%.
Table XXXIX gives the analytical results for a number of bituminous coals
and anthracites. they stand.for each of the minutes, 6-7 and 7-8, it is 0-015. Hence